This invention relates to voltage-controlled oscillators.
A frequency oscillator, such as a voltage-controlled oscillator (VCO), is an important component in telecommunication and other devices. The VCO is used as a local oscillator for up/down converters in radio systems, and as a modem oscillator in virtually all wireless and cellular systems.
The VCO is often manually adjusted during manufacturing to trim the center frequency of the resonator. However, this trimming or tuning process occupies a significant portion of the cost of a VCO. Therefore, it is advantageous is to design a system in which the tuning process during manufacturing can be eliminated.
A frequency oscillator tuning process at the manufacturing stage is replaced with an adjustment of a resonant circuit in the frequency oscillator during the operation of the oscillator.
The technique utilizes a crystal oscillator, a frequency oscillator such as a voltage-controlled oscillator (VCO), and a trimmer in a phase-locked loop configuration to determine a correction voltage required for an untrimmed VCO to operate at a nominally specified frequency by adjusting an input tuning voltage for a resonant circuit.
The trimmer for adjusting an operating frequency of the VCO includes a storage element having a set of calibrated data corresponding to a set of input signals. The trimmer also includes a controller configured to utilize the set of calibrated data to provide an appropriate tuning signal for tuning the VCO to a nominally specified output frequency. In some embodiments, the trimmer involves searching a look-up table for a calibrated data corresponding to an input signal.
The frequency oscillator having the trimmer further includes
a resonant circuit configured to receive the tuning signal from the trimmer and generate a wave energy signal of a particular frequency corresponding to the tuning signal, such that the particular frequency is substantially close to a nominally specified output frequency of the oscillator.